Saline fluid flow and hydrocarbon migration and maturation as related to geopressure, Frio Formation, Brazoria County, Texas

The Pleasant Bayou geopressured-geothermal test wells in Brazoria County, Texas, display a prominent thermal-maturity anomaly in the Oligocene Anahuac and Frio Formations. Highly geopressured, more-mature shales are interbedded with hydropressured to moderately geopressured sandstones in the upper Frio and Anahuac. In contrast, shales and sandstones in the lower Frio, including the Andrau geopressured-geothermal production zone, are highly geopressured but exhibit lower thermal maturities. Vitrinite-reflectance data, supported by hydrocarbon-maturation data and anomalous concentrations of C/sub 5/ to C/sub 7/ hydrocarbons at Pleasant Bayou, indicate that the upper Frio was subjected to an extended period of hot, extremely saline, basinal fluid flow which caused the above thermal anomaly. Regional salinity studies (Morton and others, 1983) suggest that regional growth faults were the conduits for vertical basinal brine movement at depth. At shallower levels the upwelling waters migrated laterally through permeable sandstone-rich sections such as the upper Frio. Anomalously mature gasoline-range (C/sub 5/-C/sub 7/) hydrocarbons were introduced into the upper Frio by this process. Fluid influx in the lower Frio was probably limited by high geopressure, consequently maturity in the deep Frio section (greater than 14,000 ft) remained consistent with the regional geothermal gradient

Petroleum potential of the Falkland Islands offshore area

Rocks of Precambrian, Palaeozoic and Early Mesozoic ages are present on the Falkland Islands. The islands are surrounded by extensive Mesozoic-Cenozoic basins that developed as failed rift systems during the initial stages of Gondwana separation. Large tracts of acreage in three of these basins (the Falkland Plateau Basin, South Falkland Basin and North Falkland Basin) were opened for licensing for the first time in October, 1995. The area has undergone little exploration other than the acquisition of regional seismic data, and interpretations of stratigraphy and basin history are therefore somewhat conjectural. The basins are believed to contain Jurassic to earliest Cretaceous syn-rift sediments. Probable marine and lacustrine source rocks, and reservoir rocks eroded from clean Palaeozoic quartzites, are predicted to occur within this syn-rift succession. Thick argillaceous intervals probably accumulated during a post-Valanginian thermal sag phase. This sag phase was interrupted by regional uplift, particularly during the Early Cenozoic. A variety of “play” concepts can be established within each basin, and potentially large structural targets can be defined on the reconnaissance seismic data available from the area. The region is considered to be one of the World's last true “frontier” exploration areas, where large, deep, Mesozoic failed-rift basins remain to be drilled and explored